1. Field
The present invention relates to a method for adjusting the resonant frequencies of a vibrating microelectromechanical device.
2. Related Art
Vibrating masses are commonly used elements in microelectromechanical (MEMS) devices such as MEMS resonators and resonant inertial sensors. These microfabricated resonators can be used in MEMS gyroscopes to sense the rotation of the device by measuring changes in vibrational amplitudes upon rotation. In typical vibrating mass gyroscopes, the device may be driven in one axis and the vibrational amplitude sensed in another axis. An example of a resonator structure used in a MEMS gyroscope is the Disc Resonator Gyroscope (DRG) described in U.S. Pat. No. 7,347,095, entitled “Integral Resonator Gyroscope” and U.S. Patent Application Pub. No. 2007/10017287. The resonant frequencies of the device in these two axes are typically required to be identical for operation, and are designed to have common frequencies. However, the process for manufacturing MEMS resonators typically produces devices with resonant frequencies which are not precisely at the desired resonant frequency value for each vibratory axis due to production tolerances. These differences between the resonant frequencies of the MEMS resonator in the drive and sense axes are commonly called frequency splits. These splits are typically tuned into coincidence by an electronic or electromechanical means to enable device operation. Correction methods can be performed to adjust the resonant frequencies of a MEMS resonator in order to correct for frequency splits. However, such correction methods may over or under correct the resonant frequencies and thus do not produce the level of precision necessary to adequately adjust the resonant frequencies of the MEMS resonator. If the frequency split of the MEMS resonator is too large, that is, the resonant frequencies of the MEMS resonator in its operational axes deviate too much from the desired resonant frequencies coincident value, then the MEMS resonator may be inaccurate or be unsuitable for its purpose. Further, the method for implementing these corrections may be incompatible with repeatable volume manufacturing processes.
Thus, there is a need for a method to more efficiently and accurately adjust the resonant frequencies of a vibrating microelectromechanical device to reduce the frequency split of the resonator device.